Fix local variable name in sync_cmd() function

Should be underscores rather than camel case.
Add comment to the sync_cmd() function
Add view_explore_mode_quit() function to view.c

Quits view from explore mode.
Make :sync force view mode exit for the other pane

Thanks to filterfalse.
Merge branch 'quit-view-mode-on-sync'

Make :sync force view mode exit for the other pane.

Thanks to filterfalse.